1. Outline
 Fate of pyruvate (summary)
 Energy yield of glycolysis
– Anaerobic
– Aerobic
 Details of the fates of pyruvate
– Reduction of pyruvate to lactate
– Oxidative decarboxylation of pyruvate to acetyl CoA
– Carboxylation of pyruvate to oxaloacetate
– Reduction of pyruvate to ethanol
 Feeder pathways for glycolysis
– Fructose
– galactose

2. Fate of Pyruvate
 Lactate dehydrogenase
– RBC and during exercise
– Reversible in liver
– Location: cytoplasm
 Pyruvate dehydrogenase
– TPP, LA are cofactors
– Source of AcetylCoA
– Irreversible reaction
– Location: Mitochondria
 Ethanol synthesis
– In yeast, some bacteria
– Location cytoplasm

4. 1. Reduction of pyruvate to ethanol (microorganism)
• It occurs by the 2 reactions shown below:

5. Pyruvate
decarboxylase
mechanism

6. • There is no net oxidation-reduction in the
conversion of Glc into Ethanol.
• NAD+ is used first and made it later!

7. Active site of
Alcohol
dehydrogenase

8.  Pyruvate decarboxylase is present in brewer’s and baker’s yeast.
CO2 produced during alcohol fermentation is responsible for the
characteristic carbonation of champagne.
 In baking, CO2 fermentation by pyruvate decarboxylase during
fermentation of dough due to CO2 , dough rises.
 Alcohol dehydrogenase metabolizes alcohol.
 TPP carries “active aldehyde” groups
 The pyruvate decarboxylase reaction is the first reaction we see
that TPP is involved. TPP  Vit B1. If B1 is not enough

9. More about TPP
 Beriberi: swelling, pain, paralysis, death
 TPP plays an important role in the cleavage of bonds adjacent to a
carbonyl group such as the decarboxylation of alpha-ketoacids and
in chemical rearrangements involving transfer of an activated
aldehyde group from one C to another.
 The functional part of TPP is the thiazolium ring. The proton at C-2
of the ring is relatively acidic. Loss of this proton produces an active
site in TPP.
 TPP is involved in the following reactions
1. Pyruvate decarboxylase
2. Pyruvate dehydrogenase
3. Alpha-ketoglutarate dehyrogenase
4. Transketolase

10. Microbial fermentation yield other end products of commercial value:
 Lactate and ethanol are the common products of
microbial fermentation
 Not the only ones...
– In 1910, Chaim Weizmann (first president of Israel)
discovered a bacterium
– Clostridium acetobutyricum ferments starch to butanol and
acetone.
 Here comes industrial fermentation, purpose is to
make important products from readily available
material (like starch) by using microorganism.

11. Oxidation of ethanol in humans
 Alcohol is a significant source of calories in many individuals. The
metabolism of ethanol yields acetate by means of a pathway of 2
oxidation reactions.
1. Formation of acetaldehyde:
– The first oxidation in the metabolism of ethanol occurs in the liver by
alcohol dehydrogenase.
– Some acetaldehyde is formed by a microsomal ethanol oxidizing system
(MEOS) involving NADPH, O2 and cyt P450.
2. Formation of acetate:
– Acetaldehyde is further oxidized to acetate by the enzyme aldehyde
dehydrogenase.

12. Some information about alcoholism
 90% people drink alcohol.
 40-50% of male  have temporary alcohol-induced problems.
 10% male and 3-5% female  have persistent alcohol related problems
(alcoholism).
 Ethanol easily moves through cell membranes.
 12 oz beer or 4 oz wine has 10 grams of ethanol
 1 liter of wine  80 g ethanol.

13. More about alcohol
 It is a CNS depressant, decreases activity of neurons.
 It is absorbed in the mouth, esophagus, stomach, and large bowel with a
major site of absorption is small intestine.
 The rate of absorption is increased with rapid gastric emptying, absence of
proteins, fats, or carbohydrates.
 2%-20% of ethanol is excreted directly through the lungs, urine and sweat.
 The rest is metabolized to acetoaldehyde.
 The clinical significance of acetaldehyde is not known, but accumulation in
liver, brain, or other body tissues may cause organ damage.

14. 2. REDUCTION OF PYRUVATE TO LACTATE:
 Lactate formed by the action of lactate dehydrogenase is the final product of
anaerobic glycolysis.
 In exercising skeletal muscle, NADH production (by glyceraldehyde3-P and by
the 3 NAD-linked dehydrogenase reaction of the TCA cycle) exceeds the
capacity of the respiratory chain, resulting in an increase in NADH/NAD that
favors reduction of pyruvate to lactate.
 Therefore, during intense exercise, lactate accumulates in the muscle , pH
decreases  resulting in cramps. Much of the lactate eventually diffuses from
the muscle into the blood stream.
 The direction of lactate dehydrogenase reaction depends on the relative
intracellular concentrations of pyruvate and lactate and on the ratio of
NADH/NAD in the cell.
 When animal tissues can not be supplied with enough oxygen to support aerobic
oxidation of pyruvate and NADH produced in glycolysis, NAD+ is regenerated
from NADH by the reduction of pyruvate to lactate.

16. More about lactate formation
 Certain other tissues and cell types (such as retina, brain, and
RBCs) produce lactate from pyruvate under aerobic conditions.
 Lactate is the major end-product of glycolysis in RBCs.
 In tissues such as the liver and heart, the ratio of NADH/NAD is
lower than in exercising muscle. These tissues can oxidize
lactate to pyruvate.
 The cycle of reactions that includes glucose  lactate in muscle
and lactate  glucose in liver is called the Cori Cycle for Carl
and Gerty Cori whose studies in the 1930s and 1940s clarified
the pathway and its role.

17. 3. The oxidative decarboxylation of pyruvate:
 The oxidative decarboxylation of pyruvate by pyruvate
dehydrogenase is an important pathway.
 Pyruvate + NAD+ CoA  Acetyl CoA +CO2 + NADH
 This goes to TCA cycle and will be discussed later.

18. ENERGY YIELD FOR GLYCOLYSIS
A. ANAEROBIC GLYCOLYSIS:
Overall reaction:
Glucose + 2P + 2ADP  2 Lactate + 2ATP + 2H2O
1. A net of 2 mols of ATP is produced for each molecule of glc.
2. Anaerobic glycolysis, although releasing only a small fraction of
the energy contained in the glucose molecule, is a valuable
source of energy under the following conditions.
– When oxygen is decreased such as during intense exercise
– In tissues with few mitochondria – the kidney, RBCs, WBCs,
retina, and brain.
3. In anaerobic glycolysis there is no net production or consumption
of NADH. The NADH formed by glyceraldehyde 3-P
dehydrogenase is used by lactate dehydrogenase to reduce
pyruvate to lactate. Two trioses are produced for each glucose
molecule.

19. ATP consumption and production
Reaction Change in ATP per Glc consumed
1. Glc-----> Glc-6-P …………..
2. Fructose-6-P------->F1,6bisP ………….
3. 1,3 bisPglycerate--------> 3-Phosphoglycerate ………….
4. PEP---------> Pyruvate ………….
Net: ………….

20. Formation and consumption of NADH in anaerobic glycolysis:
Reaction
change in NADH
1. Glyceraldehyde 3P-----> 1,3 BisPglyceraldehyde ……………
2. Pyruvate---------------> Lactate ……………
Net NADH: ……………

21. Aerobic glycolysis:
Overall reaction:
Glc+ 2P + 2NAD+ + 2ADP  2 Pyruvate + 2ATP + 2NADH + 2H+ + H2O.
1. The direct formation and consumption of ATP are the same as in
anaerobic glycolysis, that is a net gain of 2ATP per molecule of
glucose.
2. 2 mols of NADH are produced per mol glucose. Ongoing aerobic
glycolysis requires the oxidation of this NADH by the respiratory
chain.

22. Formation of ATP in aerobic glycolysis
 Reaction Change in ATP/glc cons.
 Glc-------------> Pyruvate
 NADH--------> NAD+
 Net ATP:

30. Other monosaccarides can enter the glycolytic pathway
Fructose must be phosphorylated to enter glycolysis.
2 enzymes are responsible for this step.
a. Hexokinase has a low affinity for fructose (high Km). Unless
fructose levels of the body increases, little fructose is
converted to fructose-6-P by this enzyme. D-fructose
(present in fruits) or hydrolysis of sucrose can be
phosphorylated by hexokinase to F-6-P.
Sucrose + H2O  Fructose + Glucose
Fructose + ATP  F-6-P + ADP
In muscle and kidney, this is a major pathway.

31. Second enzyme
b. By fructokinase:
The liver (which processes much of the dietary fructose) and
the kidney have fructokinase which converts fructose to
fructose-1-P. Fructose-1-P yields glyceraldehyde and
DiOHacetoneP by aldolase B enzyme action. Two steps are
bypassed (hexokinase and PFK) and the rate of fructose
metabolism is greater than that of Glc.

33. Galactose metabolism:
Dietary source is lactose from milk or milk products.
Lactose  Glc + Galactose
Dietary disaccarides are hydrolyzed to monosaccarides
by enzymes lining the small intestine.
– Maltose  2D-Glc
– Lactose  D-Glc + D-Gal
– Sucrose  > D-Glc + D-Fructose
– Trehalose  2D-Glc

35. Galactose metabolism
Gal  Glc-6-P in four steps
1. Gal  Glc interconversion pathway
2. Gal-1-P then takes uridyl group
3. UDP-Gal’s Gal is then epimerized to Glc
4. Finally, Glc-1-P isomerized to G-6-P

37. Many adults are intolerant of
milk due to lactase deficiency
Lactose intolerance or hypolactasia
– Deficiency is not quiet the appropriate term
– Lactase activity declines to 5 to 10% of the level of birth
– Most Africans and almost all Asians have very low levels!
– Populations with a tradition of herding cattle (northern
Europeans) continue to express lactase gene
 Problem is diarrhea.
 Treatment is easy now: Milk products (lactose has
been hydrolyzed enzymatically) and lactase-
containing pills are widely available.

41. Galactose is highly toxic
 Galactosemia: Gal-1-P-uridyl transferase deficiency
– Fail to thrive
– Vomit
– Jaundice
– Cirrhosis
– Cataracts
 Blood Gal is high.
 The absence of the transferase in RBCs definitive
diagnosis.
 Why cataracts?

44. BSO+NACA
Grade 0

45. BSO only (grade 3)

46. Control (Grade 0)

47. NACA only (Grade 0)

49. REGULATION OF CARBOHYDRATE CATABOLISM
Carbohydrate catabolism provides:
 ATP
 precursors, building blocks of some other
biosynthetic processes
ATP level for a cell should be almost constant.
ATP production  ATP consumption
balance
We undergo lots of changes which affect metabolism
such as:
 increased muscular activity
 decreased oxygen availability
 decreased carbohydrate intake

50. more
Events alter ATP production and utilization. Since
ATP levels should be kept almost constant, we need
to regulate some enzymes in glycolysis pathway.
There are 4 enzymes that play a role in this regulation
(in liver and muscle)
1. Glycogen phosphorylase, hormonal, allosteric, Ca++
2. Hexokinase
3. PFK-1
4. PK

51. Hexokinase
 Muscle hexokinase is inhibited by Glc-6-P.
Whenever Glc-6-P is increased, this enzyme is
inhibited.
 Glucokinase is an isozyme of hexokinase (also
called hexokinase-D)
– Isozymes are different proteins that catalyze the same
reaction.

52.  PFK-1 is under complex allosteric regulation
 MOST IMPORTANT CONTROL POINT
F-6-P + ATP  F1,6 bisP + ADP
• ATP
• pH
• Citrate (key intermediate of TCA cycle)
• Fructose 2,6 bisphosphate

59. PK
 Increased ATP concentrations inhibit PK allosterically
by decreasing its affinity to its substrate. PEP
 PK is also inhibited by Acetyl-CoA.
 PEP  Pyruvate  Acetyl-CoA
 Several different forms exist (L and M)
• F 1,6 bisP activates PK to keep pace with oncoming high flux
of intermediates.
• ATP inhibits, enough energy!
• Alanine also inhibits PK
• Reversible phosphorylation of the enzyme also controls this
enzyme’s action.

62. Family of Glc transporters
 Common structure:
– 12 transmembrane segments
 The members of this family have some distinctive
roles:
• glut1 and glut3
• glut2
• glut4
• glut5

66. Cancer and glycolysis
Tumors have high rate of glc uptake
and glycolysis
Why?
Hypoxic area in tumors
Consequences of the adaptation